The present invention relates generally to liquid pipetting systems and, more particularly, to a method and apparatus for coupling a replaceable pipette tip to a syringe nozzle of such a liquid pipetting system.
A pipetting syringe typically utilizes replaceable pipette tips, thereby providing a means for preventing contamination by allowing the user to switch pipette tips prior to using the syringe with a different fluid. Replaceable pipette tips, however, place several demands on both the tip and the syringe nozzle. First, the pipette tips must be easily replaced, thus promoting rapid tip exchange and efficiency of use. Second, a good seal must be formed between the inner surface of the pipette tip and the outer surface of the syringe nozzle. If a good seal is not formed, the quantity of fluid withdrawn or expelled by the syringe may be different from the intended quantity. Third, the seal quality must be consistent in order to insure run to run accuracy.
Replaceable pipette tips are either manually or automatically forced onto the syringe nozzles. Although manual attachment allows the user to monitor tip seal quality, inconsistencies in the amount of force used to couple the tip, hasty or careless tip application, and differences between users, can lead to experimental errors. Additionally, manual attachment is a relatively slow technique and therefore is too inefficient for many applications. Accordingly, automated tip replacement is preferred for those applications utilizing multi-well plates or other mass testing means as this technique allows tips to be replaced quickly. Unfortunately this technique is prone to seal errors. This sealing problem is exacerbated by the difficulties associated with monitoring tip seal quality, especially when a large number of pipettes are in close proximity to one another as is typically the case with a multi-well pipetting system.
Accordingly, what is needed in the art is a pipette tip and syringe assembly that consistently achieves a good tip seal and which can be used in an automated system. The present invention provides such an assembly.
The present invention provides a pipette nozzle that achieves a consistently high quality seal between the nozzle and the interior surface of a replaceable pipette tip. In one aspect, the end portion of the nozzle is tapered. The tapered nozzle aids pipette tip engagement in an automated system by relaxing the tolerance on the co-location of the pipette tip and the syringe nozzle. Additionally, the tapered end portion promotes tip sealing. In another aspect of the invention, a small ridge is located on the tapered portion of the nozzle. The ridge forms a seal with the interior surface of the pipette tip. The ridge, in combination with the tapered portions of the nozzle located on either side of the ridge, create three separate interface regions.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.